1. Field of the Invention
The present invention relates to a data receiving technique in which bit data included in bit stream data inputted as a bit stream is received by using a strobe signal, and more particularly, to a timing adjustment technique for a strobe signal.
2. Description of the Related Art
In order to transmit/receive data between semiconductor integrate circuits through a small number of data transmission lines, serial data transmission is used. Reception of the serial data can be executed by latching each bit data included in the serial data by a strobe signal synchronized with the bit data.
A semiconductor test apparatus (also simply referred to as a test apparatus) that tests a semiconductor circuit outputting serial data as a DUT (Device Under Test) will be considered. In this case, an unexpected delay may occur in the serial data or a clock due to a variation in wire lengths or influence of a parasitic capacitance, which occur in the DUT and the test apparatus. In order to accurately receive the serial data in such circumstances, it is needed that an edge timing of the strobe signal is adjusted so as to satisfy set-up time and hold time conditions of a latch circuit. Patent Documents 1 and 2 disclose related arts.
[Patent Document 1] Japanese Patent Application Publication No. Hei 2-62983
[Patent Document 2] Japanese Patent Application Publication No. 2007-17257
In the case where a plurality of channels of serial data are inputted to a test apparatus, there may occur non-uniform timing deviation (hereinafter, referred to as skew) in the serial data inputted to each channel. In this case, if strobe signals having an identical timing with each other are used for latching each channel of bit data, there is a fear that the set-up time and hold time conditions may be satisfied in a channel, while timing-violation occur in another channel.
When a bit rate for serial data transmission is high, the set-up time and hold time conditions become severe, and hence it is needed that the timing of the strobe signal is independently calibrated with respect to every channel in order to accurately receive all channels of the serial data. Herein, if a calibration period necessary for adjustment of one channel is long, a test period becomes long, resulting in decreased productivity. Also, when receiving a single channel of the serial data, it is preferable that calibration is executed in a shorter time. Such a problem exists in common among various data subjected to bit-stream transmission without being limited to serial data.